Since the coalbed methane is mainly adsorbed in pores of a coalbed in an adsorption state, during an exploitation of the coalbed methane, a pressure of the coalbed is mainly reduced by extracting water in the coalbed. When the pressure drops to a certain extent, gases adsorbed in the coalbed are resolved and converted into free gases. Next, the free gases are diffused into a coalbed methane well through fractures in the coalbed to realize the exploitation of the coalbed methane. However, some coalbeds have low permeabilities, i.e., they are low-permeability coalbeds, it is difficult for the free gases to be diffused into the coalbed methane well, resulting in a low exploitation efficiency of the coalbed methane in the low-permeability coalbeds. Thus, an exploitation method for coalbed methane in a low-permeability coalbed is urgently needed.
In the related arts, in low-permeability coalbeds around a coalbed methane well, caves are constructed by means of deviated directional drilling to form a coalbed stress concentration area. During coalbed stress equalization, the coalbed stress in the low-permeability coalbed is released, while the low-permeability coalbed undergoes tensile and shear failures, thereby generating new fractures, and forming gas diffusion channels through which the free gases flow into the coalbed methane well to achieve an efficient exploitation of the coalbed methane.
However, the release space for the coalbed stress in the low-permeability coalbed is limited after the transformation of the low-permeability coalbed by constructing the caves by means of deviated directional drilling, the diffusion channels formed in the low-permeability coalbed are not obvious, and the exploitation efficiency of the coalbed methane is not significantly improved.